ABSTRACT

Williams, H.; Van Hoang, L.; Elliott, P.; Nguyen, H.H., and Manh, H., 2019. A tentative record of mid-Holocene sea-level highstand and barrier overwash from the Cam River mouth, Vietnam. Journal of Coastal Research, 35(4), 852–860. Coconut Creek (Florida), ISSN 0749-0208.

A freshwater coastal marsh near the mouth of the Cam River in Northern Vietnam stands 2–3 m above mean sea level and is bordered by a coastal barrier that reaches about 6 m above mean sea level. A core from the marsh contains a 14-cm-thick sand and shell layer. The presence of abundant shell fragments suggests inland transport of littoral sediment, and the sand layer is tentatively identified as a washover deposit. The coast of the study area contains a beachrock standing above the modern beach and reaching to ∼4 m above mean sea level. A tentative explanation of this beachrock is that it represents a beach that formed during a mid-Holocene 2–3-m highstand, evidence for which has been reported from Thailand, Malaysia, Singapore, and Vietnam. Possible explanations of the sand and shell layer include the following: it is a late-Holocene tropical cyclone washover deposit, formed by a large storm surge that overtopped the coastal barrier; or it is a late-Holocene tsunami deposit formed when a tsunami wave, probably from a nearby source, overtopped the coastal barrier. The lack of other distinctive washover deposits in the core suggests that overwash of a magnitude that formed the relatively thick sand and shell layer is a rare event at this site within the last 3000 years. Given the tentative but intriguing results of this study, further research at this site is warranted to better define the stratigraphy and age of the apparent washover deposit.

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